Patent GB-604909-A (GB)
Title: Improvements in or relating to milling machines
IPC: B23P15/34
Filed: 1944-07-24
Abstract: 604,909. Milling helical surfaces; cutters. MARTINDALE ELECTRIC CO. July 24, 1944, No. 14094. Convention date, Sept. 24, 1943. [Class 83 (iii)] In a milling machine, particularly designed for cutting spiral teeth F, Figs. 6 and 7, in rotary files or burs 73, the bur is carried by a rotary spindle in a head 62, Fig. 1, and is fed axially by a hand lever 31 relatively to a stationary cutter 20 whilst being rotated about its axis. The work is secured by a collet 72, Fig. 2, in a sleeve 69 angularly adjustable within a hollow rotary spindle 66 mounted in bearings 65 in the head 62. A lever 78 pivoted on a bracket 80 attached to spindle 66 carries a pawl 77 normally pressed by a spring into contact with a notched index plate 75 secured to the sleeve 69 so that the work may be indexed within the spindle for cutting the teeth F in succession. The head 62 is adjustably secured by a screw and slot 63 to a table 51 which is angularly adjustable about a pivot 53 on a slide 28. The table is slotted at 56 to allow the position of the pivot to be varied and the angular setting is determined by a spring latch 57 on the table engaging one of the notches 59 on an arcuate plate 60 attached to the slide. The slide 28 is movable by a rack 29 and pinion 30 attached to the hand lever 31 on guides 26 carried by a shelf 25 vertically slidable on fixed guides 22 by means of a rack 32 and a pinion 33 journalled on a vertical projection 23 of the shelf and rotatable by a hand lever 37. Adjustable gibs are provided on the slides 25, 23 to take up wear, and the vertical and horizontal movements are limited by screwed rods 46, 38 carrying adjustable stop collars 49, 41. The milling cutter 20 is driven by an electric motor 21 and is carried by a spindle in a head 18 slidable axially by a screw and hand wheel 19 on a block which is angularly adjustable about a vertical pivot on a plate 14 movable on horizontal guides transverse to the cutter axis. The plate is capable of being locked in its adjusted position and is provided with an arcuate series of holes' 17 for locking the spindle head 18 in its angular setting. In operation, a workpiece 73 is inserted in the collet 72 and is located axially by an adjustable stop 105 on a member 106 pivoted on a bracket 101 adjustable on the slide 28 and capable of being swung into line with the work. The collet is then closed by hand rotation of a screwed draw-spindle 74 and, with the table 51 set parallel with the slide 28, the operator actuates lever 31 to move the work axially past the cutter 20 whilst it is lowered clear of the cutter as shown. The operator then actuates lever 37 to raise shelf 25 and bring the work into contact with the cutter, this movement being limited by the upper surface of a cam 95 engaging an adjustable roller 97 carried by a block 98 vertically adjustable on guides 99 by a screw and hand wheel 100. The lever 31 is next actuated to move the work axially' rearward in contact with the cutter and continued pressure on lever 37 maintains the cam 95 in contact with roller 97 to allow the work to rise during its axial movement in accordance with its longitudinal profile. During this longitudinal movement a pinion 86 journalled in a housing 83 on the table 51 rolls along a rack 87 pivoted at 88 to the shelf 25, thereby rotating its shaft to which is secured a bevel gear 85 meshing with a pinion 68 attached to the work spindle 66. This rotates the work to impart the helical formation to the teeth thereon. The workpiece shown, which may have a different shape such as cylindrical, conical, spherical, &c., has five fields of teeth F, each field being similar and having a tooth L which extends to the end P of the work whilst the remaining teeth are progressively shorter in each field and terminate at the long tooth of the adjacent field. In this way the teeth remain of approximately constant depth throughout their length and their wear during use is evenly distributed. The operation described above cuts one of the teeth L, and after lowering the work and returning slide 28 to its forward position, the operator indexes the work through one-fifth of a revolution within spindle 66 by releasing the pawl 77 through hand lever 78. The remaining long cuts L are then made and the cam 95 is rotated to bring another lobe under roller 97 to suit the profile of the next shortest tooth. Table 51 is also adjusted about its pivot 53 to suit the different helix angle of this tooth and successive traverses of slide 28, with indexing of the work, are performed to produce the five shorter teeth. The operations are repeated with indexing of cam 95 and angular adjustment of table 51 until all the teeth have been cut. A final finishing cut is taken over all the teeth, beginning at the point of the work and lowering the latter out of contact with cutter 20 when slide 28 is moved in the forward direction.